perf(jetbrains): eliminate fixed waits from session tests

[markijbema]

Summary

Replace repeated fixed sleeps in JetBrains session test fixtures with deterministic FIFO coroutine barriers that continue draining the IntelliJ EDT. This preserves real background-thread and Swing behavior while avoiding the 500 ms minimum cost paid by nearly every controller and session UI synchronization point.

Batch header fixture and timeline events where intermediate states are irrelevant, while retaining per-token flush boundaries in the stream deduplication regression test. Test scopes now use dedicated background dispatchers and wait for cancellation before fixture teardown to keep synchronization deterministic and prevent work leaking between tests.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• packages/kilo-jetbrains/frontend/src/test/kotlin/ai/kilocode/client/session/SessionUiTestBase.kt
• packages/kilo-jetbrains/frontend/src/test/kotlin/ai/kilocode/client/session/controller/SessionControllerTestBase.kt
• packages/kilo-jetbrains/frontend/src/test/kotlin/ai/kilocode/client/session/controller/SessionUpdateQueueTest.kt
• packages/kilo-jetbrains/frontend/src/test/kotlin/ai/kilocode/client/session/ui/header/SessionHeaderPanelTest.kt

Replaces fixed delay() sleeps with deterministic FIFO coroutine barriers using single-thread dispatchers. The await() helpers drain the dispatcher + EDT deterministically with 5-second timeout safety nets. Batching avoids unnecessary intermediate flushes; the stream dedup test retains per-token flush boundaries. tearDown() correctly cancels scope, awaits completion, and closes the dispatcher.

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_{Reviewed by deepseek-v4-pro-20260423 · 271,528 tokens}

_{Review guidance: REVIEW.md from base branch main}